42 patients with definite or classic rheumatoid arthritis were treated with an enzyme mixture (Wobenzym) for 6 weeks. Circulating immune complexes were investigated with a Clq-solid phase RIA in weekly intervals and also rheumatoid factors were determined together with other routine laboratory tests. The condition of patients after therapy was recorded together with amount of circulating immune complexes during treatment. 26 (61.9%) patients improved, 13 (30.9%) patients remained unchanged, and 3 (17.1%) showed impairment. No side effects were observed. Patients who primarily showed no immune complexes or patients who had immune complexes which became negative during enzyme therapy, showed improvement more often than patients which had immune complexes and remained positive during the entire course of therapy.